Known friction clutches provide a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. The basic clutch structure includes a clutch cover, a pressure plate, a driven disc and a flywheel. A clutch housing encloses the clutch and connects the engine block with the transmission housing. The clutch cover is fixed to the flywheel which is in turn fixed to the engine crankshaft. The pressure plate is rotatably fixed but axially displaceable with respect to both the flywheel and the cover. The driven disc is rotatably fixed to an input shaft of the transmission by a splined connection. The driven disc is axially trapped between the flywheel and the pressure plate. The driven disc has friction facing elements on opposite sides of a radially outer disc element for engagement with the flywheel and the pressure plate. The pressure plate is axially biased toward the flywheel by one or more clutch springs to compress the driven disc therebetween, causing the driven disc to rotate as a unit with the pressure plate and flywheel.
A vehicle operator can selectively release the clutch to allow relative rotation between the input shaft and the engine by displacing a floor mounted clutch pedal with their foot. Displacement of the pedal, transmitted through a linkage, effects an axial movement of a clutch release assembly. The clutch release assembly engages the radially innermost tips of clutch levers or diaphragm spring fingers. Displacement of the tips of the levers or fingers, achieved by employing the release assembly, relieves the spring load exerted against the pressure plate.
The amount of displacement of the tips of the levers or fingers necessary to achieve a complete release of the clutch varies with the type and quantity of driven discs employed. A first amount of displacement is associated with a single disc having non-cushion facing elements. An increased amount of displacement is required when the disc has cushion facing elements. Cushion facing elements facilitate the modulation of clutch reengagement and are commonly used in passenger car clutches.
In certain heavy duty applications, two driven discs are employed in one clutch, with an intermediate plate disposed between the two driven discs.
Commonly, both a cushioned system and a dual disc system are comprised of many of the same components as the single disc non-cushioned system. The same clutch, linkage and clutch housing are used. The same flywheel and pressure plate may also be used. Such commonality makes the production of clutch systems less expensive. For a dual disc clutch to accommodate the extra thickness of the driven disc and intermediate plate, a different cover or a spacer plate is commonly employed. An additional accommodation for a dual disc clutch is the use of a shorter release assembly so that the linkage mounting location on the clutch housing does not need to be shifted.
It is also necessary to modify the clutch to compensate for the increase in axial travel of the release assembly that is required to achieve complete release when switching from a single non-cushion disc system to a single cushion disc system or to a two disc system. More axial displacement or lift of the pressure plate is required to achieve complete release of both a single cushion disc system and a two disc system than a single non-cushion disc system. The amount of axial travel needed for both a single cushion disc system and a two disc non-cushion system is about the same. Yet more displacement is required when both driven discs in a two disc clutch are of the cushioned variety. The increased axial displacement has in the past been achieved by altering the internal characteristics of the clutch so that the amount of release assembly travel can remain the same for both single disc and two disc systems. This approach allows the same linkage to be used for both single disc and two disc systems. Using a single release bearing travel distance is enabled by revising one or more internal elements of the clutch, including the cover, the diaphragm spring, or levers and/or the pressure plate to provide the necessary pressure plate displacement for the amount of release bearing travel available.
However, the use of different elements in the clutch structure is considered undesirable, as it results in a proliferation of parts for manufacturers of clutches.
It is desired to provide a mechanism which enables the use of an increased number of common components for a plurality of clutch disc configurations.